The present invention relates to a liquid-crystal display device having sub-pixels thereof, corresponding to three different colors and arranged in a delta pattern, and to electronic equipment incorporating the liquid-crystal display device.
Liquid-crystal display devices find widespread use in electronic equipment, such as small computers, digital cameras, and portable telephones. Such a liquid-crystal display device typically includes a pair of opposing substrates with a liquid crystal encapsulated therebetween, and electrodes formed on each of opposing surfaces of the substrates. The two electrodes and the liquid crystal sandwiched therebetween constitute pixels arranged in a matrix. When a voltage is selectively applied across the electrodes constituting the pixel, the liquid crystal changes its alignment, controlling the quantity of light transmitted therethrough, and thereby presenting a dot.
To present a color display in the liquid-crystal display device, one pixel is divided into three sub-pixels respectively corresponding to the primary colors of R (red), G (green), and B (blue). These sub-pixels placed in a predetermined pattern are arranged in a matrix. The coloring of each sub-pixel is typically performed through a color filter formed on one of the substrates.
Known as the arrangements of the color sub-pixels, i.e., the arrangement of color layers in the color filter in the liquid-crystal display device are an RGB stripe pattern shown in FIG. 15, an RGB mosaic pattern shown in FIG. 16, an RGGB mosaic pattern shown in FIG. 17, and an RGB delta pattern shown in FIG. 18. In these figures, xe2x80x9cRxe2x80x9d, xe2x80x9cGxe2x80x9d, and xe2x80x9cBxe2x80x9d represent colors provided by respective sub-pixels. Specifically, xe2x80x9cRxe2x80x9d represents red, xe2x80x9cGxe2x80x9d represents green, and xe2x80x9cBxe2x80x9d represents blue.
The RGB stripe pattern shown in FIG. 15, also called a trio pattern, is useful for presenting a data display for texts and lines. The resolution thereof is lower than those of other patterns.
The RGB mosaic pattern shown in FIG. 16 presents a difference in display quality between a rightward rising slant line and a leftward rising slant line, thereby generally presenting slant line noise over an entire image. Particularly, when the number of sub-pixels is small, the noise becomes conspicuous.
The RGGB mosaic pattern shown in FIG. 17 is said to present a high resolution because the number of xe2x80x9cGxe2x80x9d sub-pixels providing a high visibility is large. But the score through subjective assessment tests is not necessarily high. Furthermore, if a viewing distance is small, the coarseness of an image stands out, because the number of xe2x80x9cBxe2x80x9d and xe2x80x9cRxe2x80x9d sub-pixels is small.
The RGB delta pattern shown in FIG. 18 presents a horizontal resolution 1.5 times as good as that of the RGB mosaic pattern. The RGB delta pattern shown in FIG. 18 is said to have a drawback in the presentation of the outline of an image, compared with the RGGB mosaic pattern, because of a poor slant component of the resolution thereof. However, the subjective assessment tests give the highest score to the RGB delta pattern.
Given the same density of the sub-pixels, the comparison of the patterns shows that the RGB delta pattern providing a high horizontal resolution is considered as an adequate pattern for resulting in a high-definition and high-quality image.
The following two wiring patterns are known to connect sub-pixels to conductor lines (such as data lines or scanning lines) for driving the sub-pixels in the RGB delta pattern. Specifically, there are two wiring patterns: a wiring pattern (hereinafter referred to as a type 1) in which a single data line 212 is connected to the pixel electrodes 234 of two colors of the three sub-pixels of the three RGB colors as shown in FIG. 19, and a wiring pattern (hereinafter referred to as a type 2) in which each line is connected to the pixel electrode 234 of only a single color sub-pixel of the three RGB color sub-pixels as shown in FIG. 20. In these figures, the conductor line is a data line. As shown, a short line 220d, connecting each data line 212 to each pixel electrode 234, represents an active element, such as a TFT (Thin-Film Transistor) or a TFD (Thin-Film Diode).
In the type 1 wiring pattern (see FIG. 19), among the two sub-pixels for two colors sharing one data line 212, a variation in the potential of the sub-pixel for one color is affected by the potential of the sub-pixel for the other color. For this reason, a so-called vertical cross-talk occurs, and as a result, streak-like non-uniformity (sujimura in Japanese) occurs in a display screen. The display quality is thus degraded.
This problem is resolved by adopting the type 2 wiring pattern (see FIG. 20) in which one data line 212 handles one color. In the type 2 wiring pattern, however, if the potential of a data line 212 adjacent to a given sub-pixel varies, the potential of that sub-pixel also varies. For this reason, a so-called horizontal cross-talk occurs, creating a streak non-uniformity, and leading to a degradation in the display quality.
It is an object of the present invention to provide a liquid-crystal display device which achieves a high display quality by preventing the streak non-uniformity in the display screen arising from the vertical cross-talk and the streak non-uniformity in the display screen arising from the horizontal cross-talk, and to provide electronic equipment incorporating the liquid-crystal display device.
The streak non-uniformity is first discussed in detail before discussing the present invention.
Specifically, the streak non-uniformity in the display screen, arising from the vertical cross-talk in the type 1 wiring pattern shown in FIG. 19, is a phenomenon, which is that a dark row and a light row alternately occur every other row, when a single color pattern (solid pattern) of cyan, magenta, or yellow, i.e., respectively complementary color of xe2x80x9cRxe2x80x9d, xe2x80x9cGxe2x80x9d, or xe2x80x9cBxe2x80x9d is presented.
Now discussed is the liquid-crystal display device in a normally white mode with a white display (off) presented with no voltage applied. When a cyan display is presented, an xe2x80x9cRxe2x80x9d sub-pixel is in black (on), and a xe2x80x9cGxe2x80x9d sub-pixel and a xe2x80x9cBxe2x80x9d sub-pixel are in white (off). Data needs to be written to the xe2x80x9cRxe2x80x9d sub-pixels only.
In the type 1 wiring pattern, the data line is 212{circle around (1)} is connected to the pixel electrodes 234 of the xe2x80x9cRxe2x80x9d0 and xe2x80x9cGxe2x80x9d sub-pixels, the data line 212{circle around (2)} is connected to the pixel electrodes 234 of the xe2x80x9cGxe2x80x9d and xe2x80x9cBxe2x80x9d sub-pixels, and the data line 212{circle around (3)} is connected to the pixel electrodes 234 of the xe2x80x9cBxe2x80x9d and xe2x80x9cRxe2x80x9d sub-pixels.
The pixel electrode 234 of the xe2x80x9cGxe2x80x9d sub-pixel in the even rows are connected to the data line 212{circle around (1)} only. When data is written to the xe2x80x9cRxe2x80x9d sub-pixels in the odd rows through the data line 212{circle around (1)}, a difference between the potential of the xe2x80x9cGxe2x80x9d sub-pixels connected to the data line 212{circle around (1)} and the potential of the data line 212{circle around (1)} becomes large. For this reason, the potential of the xe2x80x9cGxe2x80x9d sub-pixels in the even rows is pulled to the writing potential to the xe2x80x9cRxe2x80x9d sub-pixels as shown in FIG. 21{circle around (1)}. This is one type of vertical cross-talks.
Since the pixel electrodes 234 of the xe2x80x9cGxe2x80x9d sub-pixels in the odd rows are connected to only the data line 212{circle around (2)} while the data line 212{circle around (2)} is not connected to the xe2x80x9cRxe2x80x9d sub-pixels, a difference between the potential of the xe2x80x9cGxe2x80x9d sub-pixels connected to the data line 212{circle around (2)} and the potential of the data line 212{circle around (2)} remains small. For this reason, the potential of the xe2x80x9cGxe2x80x9d sub-pixels is almost unaffected by the writing voltage to the xe2x80x9cRxe2x80x9d sub-pixels as shown in FIG. 21{circle around (2)}.
As a result, the root-mean-square value of the voltage applied to the xe2x80x9cGxe2x80x9d sub-pixels in the even rows becomes lower than the root-mean-square value of the voltage applied to the xe2x80x9cGxe2x80x9d sub-pixels in the odd rows. This leads to a phenomenon in which the xe2x80x9cGxe2x80x9d sub-pixels in the even rows are light while the xe2x80x9cGxe2x80x9d sub-pixels in the odd rows are dark. The same phenomenon occurs in the xe2x80x9cBxe2x80x9d sub-pixels as shown in FIG. 21{circle around (3)}, in which the xe2x80x9cBxe2x80x9d sub-pixels in the even rows are dark while the xe2x80x9cBxe2x80x9d sub-pixels in the odd rows are light.
The light and dark portions alternate every row, causing the streak non-uniformity. The same is true when the yellow display and the magenta display are presented. The streak non-uniformity occurs with the odd row and the even row being dark and light.
FIG. 21{circle around (1)}, FIG. 21{circle around (2)}, and FIG. 21{circle around (3)} respectively show the potentials of video signals of the data lines 212{circle around (1)}, 212{circle around (2)}, and 212{circle around (3)} shown in FIG. 19 with the abscissa representing time, when a cyan solid pattern is presented. Although voltage modulation is applied to the video signal as shown, the same is conceptually true of a pulse width modulation (PWM), which is a standard driving method in the liquid-crystal display device employing TFD.
The vertical cross-talk is created because a single data line 212 is connected to the pixel electrodes 234 for the two color sub-pixels. Such a vertical cross-talk must be eliminated by adopting the type 2 wiring pattern shown in FIG. 20.
However, the type 2 wiring pattern has its own problem, i.e., the streak non-uniformity caused by the horizontal cross-talk. This problem is more pronounced when one of the complementary colors of xe2x80x9cRxe2x80x9d, xe2x80x9cGxe2x80x9d, and xe2x80x9cBxe2x80x9d (i.e., cyan, magenta, and yellow) is presented. Specifically, the streak non-uniformity attributed to the horizontal cross-talk is the phenomenon that the xe2x80x9cGxe2x80x9d sub-pixels in the odd rows are lighter than the xe2x80x9cGxe2x80x9d sub-pixels in the even rows while the xe2x80x9cRxe2x80x9d sub-pixels in the even rows are lighter than the xe2x80x9cRxe2x80x9d sub-pixels in the odd rows, when a yellow display is presented with the xe2x80x9cBxe2x80x9d sub-pixel in black (on) and the xe2x80x9cRxe2x80x9d and xe2x80x9cGxe2x80x9d sub-pixels in white (off) as shown in FIG. 20.
The inventors of this invention have studied the wiring pattern, and have observed that the streak non-uniformity attributed to the horizontal cross-talk is the phenomenon that the sub-pixels, surrounded by the data line 212{circle around (5)} (the data line connected to xe2x80x9cBxe2x80x9d sub-pixels) working to present a black display (namely, the xe2x80x9cGxe2x80x9d sub-pixels in the odd rows and the xe2x80x9cRxe2x80x9d sub-pixels in the even rows) are light while the sub-pixels surrounded by the data lines 212{circle around (4)}) and 212{circle around (6)} not working to present a black display (namely, the xe2x80x9cGxe2x80x9d sub-pixels in the even rows and the xe2x80x9cRxe2x80x9d sub-pixels in the odd rows) are dark.
A macroscopical observation of the phenomenon shows that alternately appearing light vertical lines (GRGR) and dark vertical lines (RGRG) are recognized as vertical streaks. The inventors have also observed that the sub-pixels, surrounded by a data line working to write black data, appear light while the sub-pixels surrounded by a data line not working to write black data appear dark when the display color is changed to a cyan display (with the xe2x80x9cRxe2x80x9d sub-pixels in black) or a magenta display (with the xe2x80x9cGxe2x80x9d sub-pixels in black). Depending on the pitch of the sub-pixels, the same phenomenon can be recognized as a horizontal streak.
To further study the phenomenon, the inventors has measured the VT curves (voltage-transmittance characteristics) of the sub-pixel of interest with the conditions of the sub-pixels surrounding the sub-pixel of interest varied. FIG. 22 and FIG. 23 show the measurement results. FIG. 22 shows an off (white) waveform measured at a xe2x80x9cGxe2x80x9d sub-pixel positioned in an even row, and FIG. 23 shows an on (black) waveform measured at a xe2x80x9cGxe2x80x9d sub-pixel in an even row. These two figures show the variations in the waveforms of the xe2x80x9cGxe2x80x9d sub-pixels which are measured when the xe2x80x9cRxe2x80x9d sub-pixels and the xe2x80x9cBxe2x80x9d sub-pixels, adjacent to the xe2x80x9cGxe2x80x9d sub-pixels of interest, are changed between on (black) and off (white) displays.
From the VT curve shown in these figures, the voltage applied to the xe2x80x9cGxe2x80x9d sub-pixels in the even row tends to shift to a high voltage side regardless of the white or black state of the xe2x80x9cBxe2x80x9d sub-pixels, when the xe2x80x9cRxe2x80x9d sub-pixels are in black. When the xe2x80x9cRxe2x80x9d sub-pixels are in white, the voltage of the xe2x80x9cGxe2x80x9d sub-pixels tends to shift to a low voltage side. This tendency is pronounced in the off (white) waveforms shown in FIG. 22. This shift in optical characteristics agrees with the phenomenon observed through the naked eye. When V50 values (i.e., the voltage at a transmittance of 50%) are compared under conditions of R: white/B: white and R: black/B: black, a difference of 1.4 V is noticed in FIG. 22, and a difference of 1.8 V is noticed in FIG. 23.
These measurement results suggest that the wiring for driving a certain sub-pixel for one color (for instance, an xe2x80x9cRxe2x80x9d sub-pixel), routed around a sub-pixel (for instance, a xe2x80x9cGxe2x80x9d sub-pixel) adjacent to the xe2x80x9cRxe2x80x9d sub-pixel, creates a parasitic capacitance, causing a variation in the ratio of effective capacitances, and thereby leading to a shift of the voltage applied to the sub-pixel.
Referring to FIGS. 22 and 23, the reason why the VT curve of the xe2x80x9cGxe2x80x9d sub-pixels in the even row is controlled by the light state of the xe2x80x9cRxe2x80x9d sub-pixels is that a data line 212{circle around (6)} connected to the xe2x80x9cRxe2x80x9d sub-pixel is chiefly capacitively coupled with the xe2x80x9cGxe2x80x9d sub-pixels, and the voltage variation affects the voltage applied to the xe2x80x9cGxe2x80x9d sub-pixels. Since the lightness of the sub-pixel is affected from the sub-pixel adjacent thereto in row, this phenomenon is called a horizontal cross-talk.
When the wirings on the element side are data lines and the electrodes on the opposing substrate side (i.e., the color filter side) are scanning lines in the liquid-crystal display device employing TFD as an active element, a data line for driving one sub-pixel is present to one of the right and the left of the sub-pixel, and a data line for driving a sub-pixel for another color is present to the other of the right and the left of the sub-pixel. The horizontal cross-talk can therefore develop not only in the delta pattern but also in other patterns, such as a mosaic pattern and a stripe pattern.
The inventors have measured the VT curve for a sub-pixel in a liquid-crystal display device having color sub-pixels arranged in a mosaic pattern, given the same number and pitch of sub-pixels. The inventors have certainly observed that the voltage shift takes place as in the same way as in the delta pattern. The streak non-uniformity, which is observed as a serious problem in the delta pattern, is not problematic in the mosaic pattern. This is because there is no clear distinction between the odd rows and the even rows in the mosaic pattern, and the entire mosaic pattern is uniformly affected. The horizontal cross-talk therefore becomes conspicuous as a problem unique to the delta pattern.
In other words, the horizontal cross-talk observed in the delta pattern in the type 2 wiring pattern is basically unrelated to the arrangement of the color sub-pixels. The effect of the horizontal cross-talk, if uniformly distributed over the color sub-pixels, is not considered as a problem in the display. It is important that the colors of the sub-pixels driven by a wiring coupled with the sub-pixels be not alternated each row. Even if the effect of the horizontal cross-talk is uniform over all sub-pixels, the type 1 wiring pattern possibly presenting the vertical cross-talk as already discussed cannot be adopted.
In this situation, the inventors have studied a new wiring pattern in which the three color sub-pixels of xe2x80x9cRxe2x80x9d, xe2x80x9cGxe2x80x9d, and xe2x80x9cBxe2x80x9d are connected to a single data line in a delta pattern. We have contemplated three types, i.e., type 3 shown in FIG. 24, a type 4 shown in FIG. 25, and a type 5 shown in FIG. 1. We have assessed the degree of influence of coupling on the sub-pixel in each of the three types of the wiring patterns. FIG. 5 shows the assessment results.
In the assessment results, the degree of influence is xe2x80x9c2xe2x80x9d when the pixel electrode of a sub-pixel of interest is surrounded on half of the four sides thereof, xe2x80x9c1.5xe2x80x9d when the pixel electrode is surrounded in an L configuration of sides thereof, and xe2x80x9c1xe2x80x9d when a straight line (one side only) thereof is surrounded. Also in the assessment results, the influence of a data line (left line), positioned left to the pixel electrode of the sub-pixel of interest, is minus, while the influence of a data line (right line), positioned right thereto is plus. Also examined is not only a difference (range) between the minimum value and the maximum value of the degree of influence but also a maximum variation in the degree of influence during scanning period of adjacent sub-pixels.
In the type 3 wiring pattern shown in FIG. 24 and the type 4 wiring pattern shown in FIG. 25, the colors of sub-pixels driven by a data line coupled with the sub-pixels of one color change every six rows and are not desirable in view of the horizontal cross-talk, for the same reason why the type 2 wiring pattern (see FIG. 19) is not desirable.
The type 5 wiring pattern shown in FIG. 1 is most desirable in view of the assessment results of the degree of coupling influence and from the standpoint of prevention of the creation of cross-talk. A first invention relates to a liquid-crystal display device having sub-pixels respectively corresponding to three different colors and arranged in a triangular configuration. A conductor line for applying a voltage to these sub-pixels is connected to pixel electrodes of the sub-pixels for the three colors in a predetermined order in a periodic pattern, while pixel electrodes commonly connected to a single conductor line are arranged on the same side of the conductor line. In this arrangement, any given sub-pixel is connected to one of two conductor lines on both sides thereof, and each sub-pixel is coupled with the conductor line on only the other side thereof. When the same color sub-pixels in each row are observed, the colors of the sub-pixels driven by the data line coupled with the sub-pixels remain the same in each row. Since the effect of the horizontal cross-talk is uniform over all sub-pixels, the liquid-crystal display device is free from the streak non-uniformity and presents an excellent display quality.
In accordance with the first invention, the configuration of the conductor line surrounding the pixel electrode is different from row to row. If the distance between the conductor line and the pixel electrode adjacent thereto remains equal among rows, the coupling capacitance between the conductor line and the pixel electrode becomes different from row to row. In the first invention, the conductor line is a data line, and as the length of a portion of the data line extending along the pixel electrode gets longer, the distance between the data line and the pixel is preferably longer, or the data line is preferably narrower in width. In this arrangement, the coupling capacitance between the data line and the pixel electrode adjacent thereto is made uniform, and a display free from the streak non-uniformity thus results.
In accordance with the first invention, considering that the number of colors employed for the delta pattern is xe2x80x9c3xe2x80x9d, the conductor lines are preferably connected to the pixel electrodes in a pattern which is periodically repeated with a multiple of six pixel electrodes.
In accordance with the first invention, the conductor line is preferably connected to the pixel electrode via an active element, and the active element is preferably fabricated of a thin-film diode having a conductor/insulator/conductor structure. With the active element, the sub-pixel to be on and the sub-pixel to be off are electrically isolated from each other. A uniform display image is thus obtained even when is used the thin-film diode, as the active element, which has difficulty forming a storage capacitor in parallel with the pixel electrode.
A second invention to achieve the above-described object relates to electronic equipment incorporating a liquid-crystal display device having sub-pixels respectively corresponding to three different colors and arranged in a triangular configuration. A conductor line for applying a voltage to these sub-pixels is connected to pixel electrodes of the sub-pixels for the three colors in a predetermined order in a periodic pattern, while pixel electrodes commonly connected to a single conductor line are arranged to the same side of the conductor line. The electronic equipment presents a good display free from the streak non-uniformity.
A third invention to achieve the above-described object relates to a liquid-crystal display device having sub-pixels respectively corresponding to three different colors arranged in a triangular configuration. Conductor line for applying a voltage to these sub-pixels has uniform parasitic capacitances thereof with the pixel electrodes of the sub-pixels.
Contemplated first to make uniform the parasitic capacitances with the electrodes of the sub-pixels is the arrangement in which the pixel electrode is surrounded by the conductor line connected thereto. In this arrangement, the data line coupled with the pixel electrode is only the one connected to the pixel electrode. In view of the uniform parasitic capacitance only, this arrangement is most desirable.
Contemplated second to make uniform the parasitic capacitances with the electrodes of the sub-pixels is the arrangement in which the periphery of the pixel electrode, other than a side facing an adjacent conductor line, is surrounded by the conductor line connected thereto with a spacing having a generally constant width thereacross. Although the liquid-crystal display device has one side of the pixel electrode coupled with the adjacent conductor line in this arrangement, the liquid-crystal display device has advantages of reducing the occurrence of short circuits in the manufacturing process thereof and of an increase in the aperture ratio thereof.
In accordance with the third invention, the conductor lines are preferably connected to the pixel electrodes in a pattern which is periodically repeated with a multiple of six pixel electrodes. This is because the number of colors employed for the delta pattern is xe2x80x9c3xe2x80x9d like in the first invention.
Like in the first invention, in the third invention, the conductor line is preferably connected to the pixel electrode via an active element, and the active element is preferably fabricated of a thin-film diode having a conductor/insulator/conductor structure.
A fourth invention to achieve the above-described object relates to electronic equipment incorporating the liquid-crystal display device having sub-pixels respectively corresponding to three different colors and arranged in a triangular configuration. A conductor line for applying a voltage to these sub-pixels has uniform parasitic capacitances thereof with the pixel electrodes of the sub-pixels. The electronic equipment thus presents a good display free from the streak non-uniformity.